1. Field of the Invention
The present invention relates to a linear rolling guide unit, in which a slider comprising a casing, end caps, an under seal and end seals is slidably mounted on a track rail through rolling elements.
2. Description of the Prior Art
An example of known linear rolling guide unit is shown in FIG. 10. The linear rolling guide unit, as shown in FIG. 10, comprises: a track rail 1 having raceway grooves 9 formed on both longitudinal sidewall surfaces 11 thereof; and a slider 30 slidably mounted astride the track rail 1. The slider 30 comprises: a casing 2 which is slidable relative to the track rail 1 and has raceway grooves 8 at positions facing the raceway grooves 9; rolling elements 4 rolling between the opposing raceway grooves 8 and 9 to allow their relative motion; and end caps 5 mounted to the longitudinal ends of the casing 2, the longitudinal direction being the sliding direction of the casing 2.
The end cap 5 has an end seal 6 that provides the longitudinal sealing between the track rail 1 and the slider 30. The end cap 5 is also provided with a grease nipple 18 for supplying lubricant to the sliding surfaces between the track rail 1 and the slider 30. To prevent the rolling elements 4 from coming off the casing 2, retainer bands 17 are provided to the casing 2 in such a way as to enclose these balls 4. To provide vertical sealing for a sliding portion between the casing 2 and end caps 5 and the longitudinal sidewall surfaces 11 of the track rail 1, under seals 31 are attached to the undersides of the end caps 5 and the casing 2.
The slider 30 is mounted astride the track rail 1 and freely slides along the track rail 1 through the rolling elements 4--balls that circulate along the raceway grooves 9 in the track rail 1. That is, the rolling elements 4 that travel loaded along the raceway grooves 9 of the track rail 1 are led to direction changing passages (not shown) formed in the end caps 5 and further to return passages 10 formed in the upper part of the casing 2 parallel to the raceway grooves 8. In this way, the slider 30 is allowed to slide relative to the track rail 1 by the rolling elements 4 traveling loaded between the raceway grooves 8 on the slider 30 and the raceway grooves 9 on the track rail 1.
Another example of the conventional linear rolling guide unit is shown in FIG. 11. FIG. 11 is a partly cutaway end view of the linear rolling guide unit. The linear rolling guide unit has a slider 32 mounted slidable on the track rail 1 and thus is provided with a sealing device at a sliding portion between the slider 32 and the track rail 1 to prevent leakage of lubricant and entrance of foreign matter from outside. The sealing device includes end seals 6 attached to the ends of the end caps 5 to provide longitudinal sealing and under seals 33 attached to the undersides of the casing 2 and the end caps 5 to provide vertical sealing.
An example of the conventional sealing device comprises a pair of end seals 6 provided one to each end cap 5 and a pair of under seals 31, 33 on both sides of the track rail 1, that is, two end seals 6 and two under seals 31, 33, a total of four components (this is referred to as a sealing device A; disclosed, for example, in Japan Patent Publication No. 38812/1982). In the sealing device A in general, the under seals 31, 33 are secured to the underside of the casing 2 or end caps 5 by fastening means such as screws and bolts.
The linear rolling guide unit applied to miniature linear way, however, has a drawback that because of the small size of the unit, the distance H between a base 27 on which the track rail 1 is installed and the underside 28 of the slider 32, i.e., dimension H.sub.1 (see FIG. 11), becomes very small making it difficult to use fastenings such as screws, which assure reliable fixing, in mounting the under seals 33 to the underside of the casing 2 or end caps 5. The only way to fix the under seals 33 is by bonding. Further, because the sealing device A consists of four components, the number of assembly processes becomes necessarily large increasing costs. Another disadvantage is that the sealing performance of a contact portion between the end seal and the under seal is not good enough.
Another example of the conventional sealing device has a pair of end seals and a pair of under seals formed in an integral structure, as shown in FIG. 12 (this is referred to as a sealing device B; disclosed, for example, in Japan Utility Model Publication No. 43136/1987). The sealing device B is fabricated by punching from a metal plate a core member having a pair of end plates 12 and a pair of bottom plates 13, and by bending the core member and fixing a seal member of elastic material such as plastics to the core member to form in an integral structure the end plates 12 serving as the end seals and the bottom plates 13 serving as the under seals. The end plates 12 each have a virtually U-shaped opening 7, to which is secured a seal member whose shape conforms to the external shape of the track rail 1. The bottom plates 13 are secured at their upper surface with a seal member whose cross section is a diamond. The end plates 12 are formed with mounting holes 14, through which screws are passed in fixing the sealing device B to the end caps 5. The distance between the paired end plates 12 is set equal to the overall longitudinal length of the casing 2 with the end caps 5 attached.
The sealing device B has a construction in which the end plates 12 are fixed to the end caps 5 by screws, in other words, they are not fixed to the underside of the casing 2 or end caps 5, so that even when the distance H (dimension H.sub.1) between the base on which the track rail 1 is mounted and the slider's bottom face is very small, the sealing device B can be secured to the end caps 5 by screws. In this sense, the sealing device B solves the problem experienced with the sealing device A. The sealing device B, however, has a drawback of being unable to accommodate variations in the overall length of the casing 2 and two end caps 5, i.e., dimensional errors, because the distance between the end plates 12 is constant.
Further, as mentioned above, because the sealing device B has its under seals and the end seals formed integral through workings, including punching and bending of the end plates 12 and bottom plates 13 and through fixing of sealing member to these plates, it is significantly difficult to fabricate the sealing device B with so high a precision that when assembled onto the slider, the under seals and the end seals have good sealing performance. Hence, high level of sealing performance may not be achieved. Furthermore, when it sustains even a partial damage, the sealing device B has to be replaced entirely, raising costs.